This is a supplemental grant to apply the internal perfusion technique to vertebrate rods. The method is very similar to that which has already proven successful for Limulus ventral photoreceptors. Rods from Bufo marinus will be sucked part way into a suction pipette. The inner and outer segment of the rod will then be detached mechanically. A microelectrode contained within the suction pipette will puncture the rod membrane, allowing the solution contained within the pipette to enter the rod. If this technique proves successful, we will test tow current theories about the mechanism of visual transduction, namely the hypothesis that calcium is the internal transmitter for exitation and the hypothesis that c-GMP is the transmitter.